X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Received: from fmailhost04.isp.att.net ([207.115.11.54] verified) by logan.com (CommuniGate Pro SMTP 5.2.14) with ESMTP id 3745141 for flyrotary@lancaironline.net; Sat, 04 Jul 2009 18:43:53 -0400 Received-SPF: none receiver=logan.com; client-ip=207.115.11.54; envelope-from=keltro@att.net DKIM-Signature: v=1; q=dns/txt; d=att.net; s=dkim01; i=keltro@att.net; a=rsa-sha256; c=relaxed/relaxed; t=1246747432; h=Content-Type: MIME-Version:Message-Id:Date:Subject:To:From; bh=BrnMZNtwyMyLhUBupc 853LIWuTQrRRx90DYbf0WzQs0=; b=VtBhJB3ELkNNTpoNVjU8J9XmzoFCG+Z++oGE5 jeH8fM9o7NCZp/g973uQR0zAcGHOTbu26uDwVv0cKTX1VCIuA== Received: from fwebmail13.isp.att.net ([204.127.221.113]) by isp.att.net (frfwmhc04) with SMTP id <20090704224316H0400hfjpce>; Sat, 4 Jul 2009 22:43:16 +0000 X-Originating-IP: [204.127.221.113] Received: from [65.255.68.159] by fwebmail13.isp.att.net; Sat, 04 Jul 2009 22:43:14 +0000 From: "Kelly Troyer" To: "Rotary motors in aircraft" Subject: FW: Pulsing Alternator Output Date: Sat, 04 Jul 2009 22:43:14 +0000 Message-Id: <070420092243.17586.4A4FDB0200073AB6000044B222218683269B0A02D29B9B0EBF019D9B040A05@att.net> X-Mailer: AT&T Message Center Version 1 (Mar 2 2009) X-Authenticated-Sender: a2VsdHJvQGF0dC5uZXQ= MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_17586_1246747394_0" --NextPart_Webmail_9m3u9jl4l_17586_1246747394_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit Group, Interesting info I found on a "Piper" owners site while looking for alternator modification links..............Might be of interest or helpful to anyone who has or is having this problem..................FWIW -- Kelly Troyer "Dyke Delta"_13B ROTARY Engine "RWS"_RD1C/EC2/EM2 "Mistral"_Backplate/Oil Manifold Re: Pulsing Alternator Output If you will examine the wiring diagram for your airplane, you will likely find that the battery is connected to a bus bar through the master switch. Everything that uses battery power is connected to this bus. The bus bar is a copper bar attached directly to circuit breakers behind the panel. The alternator output is connected thru the ammeter and then through the alternator circuit breaker to this bus bar. To excite the field winding of the alternator a voltage regulator receives power from the bus through an over voltage relay, the alternator field switch, and the field circuit breaker. (in series) The purpose of the voltage regulator is to regulate the output voltage of the alternator and not the battery voltage. After a little pause for reflection one will see that the point of connection to receive power to operate the field circuit should be obtained right at the alternator output terminal and not at the battery bus. An aircraft wired this way has had the voltage regulator loop normal high frequency switching characteristic (switches so rapidly the flicker is not seen) changed by the presence of the battery between the regulator and the alternator output terminal. The battery acts like a very low pass filter that lowers this swiching frequency to such a low frequency that the flicker on the bus voltage can be seen. The causes the jumping of the ammeter. It is not the ammeter's fault or the fault of any other of the components associated with the alternator. It is way the system is wired and the long wire runs involved. If you will carefully observe over a period of time, the flicker rate is subject to the state of charge of the battery. When the battery charge is low from heavy usage and little recharge, the internal resistance of the battery is higher than when fully charged. This extra resistance reduces the effect of the battery's presence somewhat and the flicker frequency increases. It may increase sufficiently so that the ammeter no longer flickers. As the battery recharges and the internal resistance drops,the observable flicker gets more pronounced again. So what can one do to improve on this situation? Three choices: 1. nothing. Ignore it. 2. obtain another ammeter that has high damping and that will mask the flickering so that you don't see it. Such an instrument may not exist. An electronic version may. There was a Piper service bulletin a few years back calling for the replacement of the ammeter. I don't know if this one called for a unit with sufficient damping to mask this condition or not. 3. Cut away the bus bar where it connects to the alternator field circuit breaker and connect the newly opened field circuit breaker terminal through a 16 gauge wire to the alternator output terminal. One might question why the field circuit goes through a switch in the first place. No switch like this is involved in automobiles. The reason is that in setting the aircraft up for a forced landing, it is desirable to be able to disable the alternator output to reduce the potential for electrical sparks should the alternator be damaged in the event. The master switch and the alternator switches are located side by side for this same reason. The overvoltage relay is required to protect the electrical system from a run-away-alternator. This would occur if the voltage regulator failed and applied full battery voltage continuously to the field winding. The alternator output voltage would rise and could destroy equipment using the bus. This condition will probably never be the subject of an AD since in spite of the poor wiring arrangement, safety or airworthyness is not involved. So you likely can't look to Piper for any aftermarket support on this conditiion. Who knows? Good luck. --NextPart_Webmail_9m3u9jl4l_17586_1246747394_0 Content-Type: multipart/related; boundary="NextPart_Webmail_9m3u9jl4l_17586_1246747394_1" --NextPart_Webmail_9m3u9jl4l_17586_1246747394_1 Content-Type: text/html; charset="utf-8" Content-Transfer-Encoding: quoted-printable
Group,
    Interesting info I found on a "Piper" owners site w= hile looking for alternator
modification links..............Might be of interest or helpful to any= one who has
or is having this problem..................FWIW
--
Kelly Troyer
"Dyke Delta"_1= 3B ROTARY Engine
"RWS"_RD1C/EC2/EM2
"Mistral"_Backplate/Oil Manifol= d

Re: Pulsing Alternator Output

If you will examine the wiring diagram for = your airplane, you
will likely find that the battery is connected to a b= us bar through
the master switch. Everything that uses battery power is = connected to this bus. The bus bar is a copper bar attached
directly to= circuit breakers behind the panel. The alternator output is connected thru= the ammeter and then through the alternator circuit breaker to this bus ba= r.

To excite the field winding of the alternator a voltage regulator=
receives power from the bus through an over voltage relay,
the alter= nator field switch, and the field circuit breaker. (in series)

The p= urpose of the voltage regulator is to regulate the output
voltage of the= alternator and not the battery voltage. After a little
pause for reflec= tion one will see that the point of connection
to receive power to opera= te the field circuit should be obtained
right at the alternator output terminal and= not at the battery bus.

An aircraft wired this way has had the = voltage regulator loop normal high frequency switching characteristic (swit= ches so  rapidly the flicker is not seen) changed by the presence of t= he battery between the regulator and the alternator output terminal. The ba= ttery acts like a very low pass filter that lowers this swiching frequency = to such a low frequency that the flicker on the bus voltage can be seen. Th= e causes the jumping of the ammeter. It is not the ammeter's fault or the f= ault of any other of the components associated with the alternator.
 
 It is way the  system is wired a= nd the long wire runs involved. If you will carefully observe over a period= of time, the flicker rate is subject to the state of charge of the battery= . When the battery charge is low from heavy usage and little recharge, the = internal resistance of the battery is higher than when fully charged. This = extra resistance reduces the effect of the battery's presence somewhat and = the flicker frequency increases. It may increase sufficiently so that the a= mmeter no longer flickers. As the battery recharges and the internal resist= ance drops,the observable flicker gets more pronounced again.

So wha= t can one do to improve on this situation? Three choices:
1. nothing. Ig= nore it.

2. obtain another ammeter that has high= damping and that
will mask the flickering so that you don't see it. Su= ch an
instrument may not exist. An electronic version may. There
was = a Piper service bulletin a few years back calling for the
replacement of= the ammeter. I don't know if this one called
for a unit with sufficient= damping to mask this condition or not.
 
3. Cut away the bus bar where it connects t= o the alternator field
circuit breaker and connect the newly opened fiel= d circuit breaker terminal through a 16 gauge wire to the alternator output= terminal. 

One might question why the field circuit goes throu= gh a switch in the first place. No switch like this is involved in automobi= les. The reason is that in setting the aircraft up for a forced landing, it= is desirable to be able to disable the alternator output to
reduce the = potential for electrical sparks should the alternator be damaged in the eve= nt. The master switch and the alternator switches are located side by side = for this same reason.

The overvoltage relay is required to protect t= he electrical system from a run-away-alternator. This would occur if the vo= ltage regulator failed and applied full battery voltage continuously to the= field winding. The alternator output voltage would rise and
could destr= oy equipment using the=20bus.

This condition will probably never be = the subject of an AD since in spite of the poor wiring arrangement, safety = or airworthyness is not involved. So you likely can't look to Piper for any= aftermarket support on this conditiion. Who knows?

Good luck.
 
 
--NextPart_Webmail_9m3u9jl4l_17586_1246747394_1-- --NextPart_Webmail_9m3u9jl4l_17586_1246747394_0--